R1:b7f6956ec94d

Allow Diviner groups to be configured in `.book` files

Summary:
Ref T988. Currently, every class/function needs to be annotated with `@group`, but 99% of this data can be inferred from file structure, at least in this project. Allow group specifications like:

"paste" : {
"name" : "Paste",
"include" : "(^src/applications/paste/)"
}

..to automatically put everything defined there in the "paste" group. A list of regexps is also supported. Depends on D6855.

Test Plan: Regenerated documentation…